Heat Exchangers and Systems Thereof

ABSTRACT

Improved heat exchangers and methods of manufacturing the heat exchangers are provided. The methods include modification of surface(s) of the heat exchanger in an integrated manner during manufacturing, to impart desired properties such as decreased corrosion, pressure drop, and water retention, and increased anti-frosting performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to PCT Application No. PCT/US2019/065978, filed Dec. 12, 2019, and claims the benefit of US Provisional Application Nos. 62/876,632, filed Jul. 20, 2019, and 63/038,693, filed Jun. 12, 2020, all of which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The invention relates to heat exchangers, in particular microchannel heat exchangers used for cooling and refrigeration manufactured via aluminum brazing technologies.

BACKGROUND

The demand for air conditioning and refrigeration is increasing due to a growing population, a globally expanding middle class with increasing purchasing power, and exceptional growth in cities or regions with high average temperatures. Further, there is a demand for higher efficiency, lower cost, and more environmentally friendly systems. Several different systems are available in the field for providing cooling service. Heat exchangers are primary components of the majority of these systems.

There are two primary types of heat exchangers in use, fin-tube heat exchangers and more recently developed microchannel heat exchangers (MCHE). Microchannel heat exchangers are better able to satisfy the increasing production and environmental demands than fin-tube heat exchangers, through lower production costs and lower refrigerant use. However, microchannel heat exchangers suffer performance degradation over time, due to water collecting in the body of the heat exchanger. Additionally, proximity to corrosive environments, such as oceans, industrial settings, or polluted air, can increase the corrosion rates and reduce component lifetime.

Typically, coatings to reduce corrosion are considered for systems in coastal proximity up to 3 km, and pollution levels >50 micrograms/m³. Corrosion coatings that do not negatively affect energy efficiency by increasing pressure drop, reducing airflow, or increasing thermal resistance between the heat exchange surface and the air are also strongly desired.

Microchannel heat exchangers are typically manufactured through a brazing process. Components are assembled and jigged together, and then flux is applied to remove oxide from the heat exchanger surfaces to be brazed, in order to improve the strength of the joint. A controlled atmospheric furnace is used to form the joints of the heat exchanger. After cooling, fluid interconnects are brazed onto the heat exchanger body, and the unit is leak tested and finally packaged for shipment to either a coating facility for application of a coating, or to a location for assembly of the heat exchanger into a system.

BRIEF SUMMARY OF THE INVENTION

In one aspect, integrated methods for manufacturing heat exchangers are provided. In some embodiments, the method includes integrating modification of one or more substrate surface of the heat exchanger with manufacture of the heat exchanger, wherein the substrate surface is modified with a surface modification material, and wherein the surface modification is performed prior to completion of manufacture of the complete heat exchanger structure. In one embodiment, the method includes: (a) depositing the surface modification material on the substrate surfaces(s) of the heat exchanger; (b) treating the deposited surface modification material to remove moisture, an anionic compound, a binder, and/or a solvent; and (c) depositing a second layer of material onto the surface modification material to provide one or more functional properties to the surface. The functional properties provided by the second deposited layer of material may include, but are not limited to, wettability, ultraviolet (UV) protection, corrosion resistance, surface energy modulation, and/or aesthetic modification.

In some embodiments, the heat exchanger is a microchannel heat exchanger (MCHE). In some embodiments, the substrate surface includes a manifold, a fin, a tube, and/or a microchannel surface.

In some embodiments, the surface modification includes an additive barrier coating method.

In some embodiments, the manufacturing method includes a brazing step and a step for attachment of fluidic interconnects, and the surface modification is conducted after brazing and prior to attachment of the fluidic interconnects. In some embodiments, preparation of the surface prior to surface modification is not required. In some embodiments, the manufacturing method includes a brazing step, and the surface modification is carried out prior to brazing. In some embodiments, the manufacturing method includes a brazing step, flux material is applied to the surface prior to brazing, and the surface modification and the flux brazing are conducted concomitantly. In some embodiments, flux material interacts with the substrate surface to remove native surface oxide and interacts with the surface modification material to remove metal oxides of the surface modification layer during brazing. In some embodiments, the flux brazing interacts with the substrate surface to remove surface oxide and does not interact with the surface modification material during brazing.

In some embodiments, the surface modification material is an inorganic material. For example, the inorganic material may include one or more element that forms an alloy with aluminum, e.g., an aluminum alloy that melts at a temperature less than about 660° C. For example, the one or more element may include, but is not limited to, silicon, zinc, magnesium, indium, copper, germanium, calcium, or a combination thereof. In some embodiments, the element(s) may include metal(s) and/or metalloid(s). In some embodiments, the element(s) may include transition metal(s), post-transition metal(s), lanthanoid(s), actinoid(s), alkaline earth metal(s), and/or alkali metal(s).

In some embodiments, the surface modification material forms a nanostructured material on the substrate surface.

In some embodiments, the surface modification material acts as a braze, flux, barrier coating, functional coating, or a combination thereof during manufacture of the heat exchanger. In some embodiments, the surface modification material is involved in the adhesion of parts of the heat exchanger. In some embodiments, the parts are adhered by brazing, ceramic bonding, or a combination thereof. In some embodiments, the parts are adhered at a temperature lower than 660° C. In some embodiments, the surface modification material provides improved brazing properties in comparison to a standard controlled atmospheric brazing process (CAB).

In another aspect, heat exchangers are provided that are manufactured according to integrated manufacturing methods as disclosed herein. In some embodiments, the heat exchanger is a microchannel heat exchanger (MCHE). In some embodiments, the heat exchanger is utilized in an air conditioning system, a refrigeration system, a filter element, or a heat pump.

In some embodiments, the surface modification material affects the condensate droplet adhesion force and in turn the wettability of the surface of the heat exchanger. In some embodiments, the surface modification material provides improved heat exchanger performance in comparison to an uncoated heat exchanger surface. In some embodiments, the surface modification material provides improved corrosion resistance in comparison to an uncoated heat exchanger surface. In some embodiments, the surface modification material provides a reduced amount of holdup liquid in the heat exchanger in comparison to an uncoated heat exchanger surface. In some embodiments, the surface modification material reduces the amount of water, condensate, frost, or ice that is maintained within the heat exchanger body during operation in comparison to an uncoated heat exchanger surface. In some embodiments, the surface modification material reduces the amount of debris or fouling material that is maintained within the heat exchanger body during operation in comparison to an uncoated heat exchanger surface.

In some embodiments, the surface modification material in the heat exchanger is an inorganic material. For example, the inorganic material may include one or more element that forms an alloy with aluminum, e.g., an aluminum alloy that melts at a temperature less than about 660° C. For example, the one or more element may include, but is not limited to, silicon, zinc, magnesium, indium, manganese, copper, germanium, calcium, or a combination thereof.

In some embodiments, the surface modification material forms a nanostructured material on the substrate surface of the heat exchanger.

In another aspect, refrigeration units are provided. In some embodiments, the refrigeration unit includes: a compressor; a microchannel evaporator coil; a microchannel condenser coil; a working fluid expansion device; and an enclosure, wherein the microchannel evaporator coil comprises a coating of surface modification material that comprises a metal oxide and/or metal hydroxide, and wherein the enclosure includes a housing capable of maintaining a predetermined temperature range across all variable seasonal temperature conditions. In some embodiments, the working fluid expansion device is a thermostatic expansion valve. For example, the enclosure may include a housing which, for example, protects the refrigeration unit and maintains a desired temperature range (e.g., a predetermined temperature range) within an area (e.g., space, region, volume) in which control of temperature is desired. The output of the system controls the temperature of the area of interest, such as a room, a house, a refrigerator, etc. In the case of a house, the housing separates the inside from the outside environment, in the case of a refrigerator, the housing separates the inside of the refrigerator from the environment outside of the refrigerator, an outdoor housing protects the equipment and houses the ducts that bring outdoor air in, etc.

In some embodiments, the coating has a thickness of less than about 20 microns or less than about 10 microns. In some embodiments, the coating increases the air-side heat transfer coefficient of the microchannel evaporator coil. In some embodiments, the microchannel evaporator coil is brazed.

In some embodiments, the surface modification results in a contact angle greater than about 120°, which appreciably mitigates the aggregation of water on the microchannel evaporator coil surfaces. In some embodiments, the surface modification results in a contact angle less than about 45° or less than about 30°, which appreciably distributes the water on the microchannel evaporator coil surfaces to reduce aggregation and pooling of the water.

In another aspect, methods are provided for coating a microchannel heat exchanger. In some embodiments, the methods include: (a) immersing said heat exchanger in a bath comprising a metal salt; (b) immersing said heat exchanger in a solution of a fluorinated-terminated or alkyl-terminated compound; and (c) allowing said heat exchanger to dry. In other embodiments, the methods include: (a) etching the surface of said heat exchanger; (b) immersing said heat exchanger in a bath comprising a metal salt; (c) immersing said heat exchanger in a solution of a fluorinated-terminated or alkyl-terminated compound; and (d) allowing said heat exchanger to dry. In other embodiments, the methods include (a) etching the surface of said heat exchanger; (b) immersing said heat exchanger in a bath comprising a metal salt; and (c) allowing said heat exchanger to dry.

In another aspect, heat pump systems are provided. In some embodiments, the heat pumps include: a compressor; a first microchannel evaporator coil; a second microchannel evaporator coil; a working fluid expansion device; and an enclosure including both a heating and cooling mode, wherein the first and second microchannel coils comprise a coating of surface modification material that comprises a metal oxide and/or metal hydroxide, and wherein the enclosure comprises a housing capable of maintaining a predetermined temperature range across all seasonal temperature conditions. For example, the enclosure may include a housing which, for example, protects the heat pump system and maintains a desired temperature range (e.g., a predetermined temperature range) within an area (e.g., space, region, volume) in which control of temperature is desired. The output of the system controls the temperature of the area of interest. In some embodiments, the working fluid expansion device is a thermostatic expansion valve.

In some embodiments, the coating has a thickness of less than about 20 microns or less than about 10 microns. In some embodiments, the coating increases the air-side heat transfer coefficient of the first and second microchannel evaporator coils. In some embodiments, the first and second microchannel evaporator coils are brazed.

In some embodiments, the direction of operation of the heat pump system can be reversed.

In some embodiments, the surface modification results in a contact angle greater than about 120°, which appreciably mitigates the aggregation of water on the microchannel evaporator coil surfaces. In some embodiments, the surface modification results in a contact angle less than about 45° or less than about 30°, which appreciably distributes the water on the microchannel evaporator coil surfaces to reduce aggregation and pooling of the water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows several design integration embodiments for methods of producing improved heat exchangers, as described herein. “Parts” or “clad parts” are used. “Jig” refers to a step to hold a loose set of parts of a heat exchanger assembly in place. “Flux” refers to exogenous addition of flux material to the parts. “Heat” refers to a thermal treatment step designed to activate the flux and promote brazing. “200” refers to surface preparation. “300” refers to deposit of surface modification material. “400” refers to thermal treatment of the surface modification material. “500” refers to further treatment of the deposited surface modification material. “600” refers to final surface treatment to provide various functional properties. “Finish” refers to addition of fluidic interconnects and fittings. “Test” refers to pressure testing of the device to ensure that the unit can maintain a desired pressure rating. “Ship” refers to shipping of assembled heat exchanger units to a next destination, such as an assembly location or for a conventional surface coating procedure.

FIG. 2 shows a sequence of images as water was sprayed on coated and uncoated surfaces for removal of cardboard lint, as described in Example 6. The upper left image represents time zero. The images are in time sequence from top to bottom, and the bottom right image represents the last time point.

DETAILED DESCRIPTION

The invention provides methods and applications for the improvement of microchannel heat exchangers (MCHE) in parameters such as corrosion, pressure drop, water retention and antifrosting performance. An integrated manufacturing processes is disclosed herein, in contrast to the traditional serial processing approach. Improved coating compositions for heat exchangers are also described herein.

Modern heat exchangers, such as microchannel heat exchangers (MCHE), can be improved through the application of surface modification. Previously, surface modification has been performed after manufacture of the heat exchanger and as such, surface modifications are limited by manufacturing/brazing byproducts such as flux residue and surface roughness from reflow of cladding materials. However, in the processes described herein, surface modification is integrated with and performed during manufacture of the heat exchanger, which allows for surface treatments and processes that are not limited by the brazing conditions, that may be applied on more uniform surfaces, resulting in higher quality parts, and/or that may be processed in a collocated rather than sequential manner, reducing costs and potential damage from additional packaging and handling. Heat exchanger components, in whole or in part, may be processed in this manner.

For example, surfaces such as manifolds, fins, and/or tubes (microchannels) of the heat exchanger may be modified during preparation and processing of loose parts, and/or the surfaces of the heat exchanger itself may be modified during brazing. Surface modification may include application of a coating composition to these surfaces in an integrated manufacturing process, for example, in a multistep coating process that is integrated with manufacture of the heat exchanger.

Coating compositions that are applied for surface modification herein may provide one or more benefits, including, but not limited to, reduction in corrosion, improved heat transfer (which may permit manufacture of smaller units), improved frost tolerance/faster defrosting, and reduced water holdup (through surface wettability changes, which may also increase longevity), in comparison to an uncoated surface in an identical heat exchanger.

The process of manufacturing MCHE typically includes sizing of materials, a loose assembly of the parts, the addition of flux to remove oxides and promote adhesion, a multistage heating step to braze the loose parts together, cooling, and addition of fluidic interconnections. Surface coatings can be applied to these heat exchangers after manufacturing to reduce corrosion or provide other benefits. However, the improved process disclosed herein integrates the surface modification processing and heat exchanger production into a single production process. Rather than completing the fabrication of the heat exchanger and then applying a coating composition, the methods disclosed herein include applying the coating in processing steps that are within the traditional heat exchanger manufacturing process, non-limiting embodiments of which are indicated in FIG. 1 and described infra.

With reference to FIG. 1, surface modifications, as described herein, include the following processing steps, or subsets thereof: (a) cleaning to ensure the substrate material to be coated is free from debris and oils, which may be present from testing, packaging and/or shipping operations (100) (not shown in FIG. 1), which may limit both the quality of the coating and reduce the longevity of production baths; (b) an optional surface preparation to prepare the surface for and promote adhesion of the surface to functional surface modification material (coating composition) (200); (c) additive deposition of functional materials (300), e.g., through immersion in a bath comprising a metal salt; (d) thermally treating the functional materials (400); (e) an optional secondary surface treatment, e.g., etching, or e.g. to provide or enhance functionality to the materials deposited in (c) or (f) or an optional step to further prepare the surface for final surface treatment in (f) (500); and (f) an optional final surface treatment, providing functional properties, such as UV protection, wettability, surface energy modulation, improved corrosion resistance, and/or aesthetic modifications (600). In some embodiments, step (a) (100) is not explicitly performed, for example, relying either on remotely cleaning processing, or alternative processing steps (e.g., brazing treatment). In some embodiments, step (b) (200) is not performed. In some embodiments, step (e) (500) is not performed. In some embodiments, steps (c) (300), (d) (400), and (f) (600) are performed, and one or more, or all, of steps (a), (b), and (e) are not performed. In some embodiments steps (c) (300) and (d) (400) are performed, and one or more, or all of steps (a), (b), (e), and (f) are not performed.

Functional surface modification materials may include, but are not limited to: metal oxide barrier coatings or other ceramic coatings such as metal oxides, hydroxides, carbonates and/or phosphates, e.g., for corrosion resistance; metal oxides and/or phosphates, e.g., for adhesion; silanes, e.g., for wetting; and/or urethanes, e.g., for UV protection. In one embodiment, step (c) includes deposition of a metal oxide and/or hydroxide layer, followed by immersion in a solution of a fluorinated-terminated, alkyl-terminated, or other compound which affects wettability (e.g., functionalized to make the surface hydrophobic).

Functional surface modifications may be used to enhance the manufacturing process. In one non-limiting example, some or all of the individual components are treated with a hydrophilic wicking material prior to the jigging and brazing process that serves a primary purpose of enhancing the wicking and distribution of flux materials to and around the joints.

Functional surface modifications may be used to enhance the resulting part performance. In one non-limiting example, the tube materials that are typically treated with zinc to modify the corrosion behavior are surface modified to alter the electrochemical potential.

Functional surface modifications may be used to enhance the manufacturing process. In one non-limiting example, some or all of the individual components are treated with a hydrophilic wicking material prior to the jigging and brazing process that serves a primary purpose of enhancing the mechanical robustness of folded coil materials.

The integration of the heat exchanger production process and the surface modification has several potential benefits, including functional modifications arising due to changes in surface energy over periods of hours, lower costs of production, and reducing shipping and packaging costs. In some embodiments, surface preparation leaves the heat exchanger surface in a low energy state appropriate for additional processing. For example, after thermal treatment, if surface energy is low, water will readily wet the surface with a contact angle less than about 20° immediately after processing. At about 6 hours, the contact angle on the same material may be about 40°, at about 24 hours, about 65°, and at about 72 hours, about 80°. The energy state of the surface is a function of the ambient environment and time since the prior processing. The surface preparation described herein may render the surface appropriate for subsequent processing such that the contact angle is less than about 20°. This state may be confirmed through the immersion and removal in a clean aqueous step and observation of the wetting characteristics. A drying of the tested part is not required before subsequent processing steps. By integrating the surface modification with the rest of the manufacturing steps, surface preparation step(s) (e.g., step (b) above, or (200) on FIG. 1), can be removed in some embodiments.

In some embodiments, the integrated surface modification as described herein permits application of a thin layer of coating material, e.g., less than about 1 mil (25 microns) in thickness, or less than any of about 20 microns, 10 microns, 5 microns, or 1 micron in thickness. The coating approach disclosed herein may provide benefits not conferred by a thick (e.g., greater than about 25 micron) coating layer, e.g., low thermal resistance and low surface stress, while at the same time providing properties desired for longevity and durability, e.g., corrosion resistance, when compared to single process step methodologies, such as spray on or dip coatings (e.g., paints, polymers) alone.

In some embodiments, the integrated surface modification includes processing of surface modification material on top of a flux material. In some embodiments, the surface modification material obviates the need for flux material. In some embodiments, the integrated surface modification includes ceramic bonding of parts of the heat exchanger.

In addition, the proposed integrated methods obviate the need for serial processing in which the nearly finished parts require an additional processing step, such as a conventionally applied coating. This serial processing requires two discrete facilities and provides opportunities for damage after QA/QC testing in the primary production facility.

In addition to optimization through process integration, additional processing approaches are disclosed that can be used to alter the manufacturing process of heat exchangers, providing additional benefits. One such example is an alternative processing method such as ceramic bonding.

Ceramic bonding can be used to make a variety of useful components. Metal oxides and/or hydroxides allow for high temperature operation, much higher than the typical aluminum to which the metal oxide and/or hydroxide is bound. For example, the metal oxide and/or hydroxide may include an oxide and/or hydroxide of an alkaline earth metal, such as, but not limited to a magnesium oxide and/or hydroxide. For example, the metal oxide and/or hydroxide may include an oxide and/or hydroxide of a transition metal, such as, but not limited to, a manganese, or zinc oxide and/or hydroxide. For example, the metal oxide and/or hydroxide may include an oxide and/or hydroxide of other metals, such as, but not limited to, an aluminum oxide and/or hydroxide. For example, ceramic bonding may be carried out with more than one metal, resulting in a mixed metal oxide and/or hydroxide. In one embodiment, the metal oxide is ZnO. Additionally, a metal based ceramic layer can create a strong bond between two metal parts, resulting in a ceramic bond with strength approaching that of a weld and many other advantageous properties, such as uniformity and conformality. The metal oxide and/or hydroxide deposition process disclosed herein provides a thin uniform layer, which provides benefit over spray type applications.

In certain embodiments, the ceramic bonding process may bond individual oxides on adjacent parts resulting in a mechanically strong, but electrically resistive joint. For example, two discrete parts or components, each containing an oxide and/or hydroxide, which may be the same (e.g., in a nonlimiting example, MgO/MgO) or different (e.g., in a nonlimiting example, MgO/ZnO), are fused or joined together to produce a single part with a common oxide and/or hydroxide (e.g., MgO) or a mixed metal oxide and/or hydroxide (e.g., MgZnO). “MO,” where “M” is a metal (in nonlimiting examples, MgO or ZnO), represents a metal oxide and/or hydroxide herein, including different oxidation and/or hydration states, if applicable. For example, MgO may refer to Mg_(x)O_(y)H_(z), where x, y, and z are present in different combinations, such as, for example, 1-1-0 for MgO, 1-1-1 for Mg(OH), 6-7-2 for Mg₆O₆*H₂O.

The process also includes coating the desired parts conformally, providing additional design freedom for the designer. Further, the ceramic bonding processing temperatures can be lower than typical brazing temperatures. Brazing requires melting of the flux and/or brazed materials, whereas ceramic bonding does not; thus, lower temperatures may be deployed.

The use of ceramic bonding provides processing benefits, including lower processing temperatures and ambient heating environments. Controlled atmosphere brazing (CAB), the most common for MCHE, occurs at temperatures no lower than 585° C., whereas ceramic bonding may occur at temperatures as low as 250° C. This lower processing temperature may provide additional benefits with regard to the underlying structures, and/or with regard to the allowable materials of construction. In some embodiments, this lower bonding temperature may allow for ceramic bonding to occur concomitantly with the flux binder removal process. In some embodiments, this lower bonding temperature may allow for ceramic bonding to occur concomitantly with application of polymers and other organic materials. Ceramic structures may be applied to facilitate uniform coverage of polymers, glues, paints, organic and other lower temperature materials, such as, for example, wicking of an adhesive or glue to ensure good contact.

Higher temperature processing results in mechanical grain growth and potential corrosion and stress induced issues at grain boundaries. The lower temperature used for ceramic bonding provides greater and easier control over the heating profile with fewer processing constraints. This increased processing tolerance, in terms of temperature and time profiles in which part adherence is maintained, maximizes part to part consistency, increasing product yield and minimizing QA/QC challenges for heat exchanger production. Ceramic bonding, as disclosed herein, may be deployed as an alternative to the CAB process. In some embodiments, ceramic bonding is lighter, stronger, and completed at lower temperature than standard CAB conditions. For example, ceramic bonding may be performed at about 100° C. lower temperature than CAB. In various embodiments, ceramic bonding is performed at any of about 100° C., 150° C., 200° C., 250° C., 300° C., 350° C., or 400° C. lower temperature than CAB (for example 250° C. versus 650° C. CAB temperature). For example, ceramic bonding may be performed at a temperature of any of about 250° C., 300° C., 350° C., 400° C., 450° C., 500° C., or 550° C., or any of about 250° C. to about 300° C., about 275° C. to about 325° C., about 300° C. to about 350° C., about 325° C. to about 375° C., about 350° C. to about 400° C.°, about 375° C. to about 425° C., about 400° C. to about 450° C., about 425° C. to about 475° C., about 450° C. to about 500° C. about 475° C. to about 525° C., or about 500° C. to about 550° C., about 250° C. to about 350° C., about 300° C. to about 400° C., about 350° C. to about 450° C., about 400° C. to about 500° C., about 450° C. to about 550° C., about 250° C. to about 400° C., about 300° C. to about 450° C., about 400° C. to about 550° C., about 250° C. to about 450° C., about 300° C. to about 500° C., about 350 to about 550° C., or about 250° C. to about 550° C.

Ceramics that may be formed using the techniques described herein include, but are not limited to, metal oxide and/or hydroxide (e.g., zinc, magnesium, manganese, or aluminum oxide and/or hydroxide) alloys and structures, such as, but not limited to, Zn—X—O alloys and structures including zinc-aluminum-oxygen spinels (X═Al), zinc silicate (X═Si), zinc-manganese-oxide (X═Mn), zinc-manganese-aluminum-oxide (X═Mn, Al), or any combination thereof. Ceramics, e.g., M-X—O, where M=a metal, are considered additional nonlimiting examples. Additional nonlimiting examples include Y—X—O, where Y═Mg and X═Al, Si, Mn, Ce, Zn, etc., or Y═Mn and X═Al, Si, Mg, Ce, Zn, etc.

Surface modification technologies, as described herein, may be applied to MCHE designs, reducing the amount of water, condensate, frost, or ice which is maintained within the heat exchanger body. This holdup water, upon freezing, leads to ice formation, and with the expansion in volume results in damage to the heat exchanger. Surface modifications resulting in a contact angle greater than about 150°, or greater than about 120°, which appreciably mitigates the aggregation of water on heat exchanger surfaces under condensing conditions, can prevent damage arising from water retention, such as frost/ice build-up, fouling, corrosion, and/or microbial growth. Surface modification is important in that it enables applications which to date have been unachievable—including refrigeration heat exchangers and outdoor coils for heat pump applications.

Surface modification technologies, as described herein, may be applied to MCHE designs, reducing the amount of debris and fouling materials which are maintained within the heat exchanger body. This material results in decreases in performance of the heat exchanger, can lead to reduced component lifetime, can serve as a source of microbial activity, can increase pressure drop of the working fluid, and can accelerate the degeneration of performance.

Unless defined otherwise herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention.

Numeric ranges provided herein are inclusive of the numbers defining the range.

Definitions

“A,” “an” and “the” include plural references unless the context clearly dictates otherwise.

“Additive,” in reference to a surface modification (coating) material herein, refers to a material is added to the substrate, in contrast to a conversion coating

“Ambient heating environment” refers to a heating environment, e.g., within a furnace, to which no adjustment is made, e.g., nitrogen not added to displace air; or no vacuum applied.

A “barrier coating” forms at least a portion of a physical barrier, thus minimizing contact with undesired elements (e.g., water (as a “moisture barrier”); e.g., electrolytes (as a “corrosion barrier”).

“Brazing” refers to a metal joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, wherein the filler material possesses a lower melting point than the adjoining metals of the joint.

The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.”

“Binder” or binding agent is any material or substance that holds or draws other materials together to form a cohesive whole mechanically, chemically, by adhesion or cohesion.

“Binderless” refers to absence of a binder that may be exogenously added to a primary material to improve structural integrity, particularly with regard to an organic binder or resin (e.g., polymers, glues, adhesives, asphalt) or inorganic binder (e.g., lime, cement glass, gypsum, etc.).

“Capillary climb” refers to a surface tension driven flow of liquid up a sample (the capillary climb is parallel to, and opposite to, the direction of the force (vector) due to gravity) upon contact with a free surface of liquid as a result of the porous substrate.

A “ceramic” or “ceramic material” refers to a solid material including an inorganic compound of a metal or a metalloid, and a non-metal, with ionic or covalent bonds. A “non-metal” may include oxygen (oxide ceramic), or carbon (carbide) or nitrogen (nitride) (non-oxide ceramics). A “metal” may include a non-hydrogen element of Group 1 of the periodic table, an element of Groups 2-12 of the periodic table, or an element from the p-block (Groups 12-17 of the periodic table), e.g., Al, Ga, In, Tl, Sn, Pb, Bi, or combinations thereof. A “metalloid” may include B, Si, Ge, As, Sb, Se, Te, or Po, or combinations thereof.

“Ceramic bonding” refers to depositing a ceramic coating composition onto two metal parts simultaneously. The coating fills in spaces between the parts, and upon thermal treatment, fuses the parts and ceramic together into one bonded piece.

A “complete heat exchanger structure” refers to a structure in which the working fluid (e.g., refrigerant) is at least partially, or completely, contained, and the fluid to be conditioned (e.g., air) is at least partially, or completely, isolated from the working fluid resulting in thermal energy exchange between the working fluid and the fluid to be conditioned. In one embodiment, the working fluid is water, which is partially contained, the fluid to be conditioned is air, and some leakage of the working fluid is used to further treat the airstream.

“Conformal” refers to a deposited composition that is uniform or substantially uniform in thickness. “Conformality” refers to the degree to which a deposited coating material has a uniform thickness, e.g., even in holes and hard to reach spots. “Conformal coating” refers to a coating composition, e.g., a thin film, that conforms to the contours of a substrate.

“Contact angle” refers to the angle measured through a liquid between a surface and the liquid-vapor interface at the contacting surface.

“Contiguous” or “contiguity” refers to pores and structures that contain walls and features in direct contact with one another or that share a common wall across a region or dimension large relative to an individual pore or structure.

“Controlled atmosphere” refers to a heating environment, e.g., within a furnace, in which the composition, pressure, and/or temperature is controlled, e.g., by adding nitrogen to displace air or applying a vacuum.

A “conversion coating” refers to a surface layer in which reactants are chemically reacted with the surface to be treated, which converts the substrate into a different compound. This process is typically not additive or a deposition, but may result in a small mass change. In a non-limiting embodiment, a conversion coating may be a ceramic non-barrier (e.g., porous ceramic) coating.

“Fluidic interconnections” refers to fluid connections that connect MCHE fluid manifolds to desired system connections. In one embodiment, a fluidic interconnection involves a small tube (e.g., copper tube) that is brazed to the manifold (e.g., aluminum manifold). In other embodiments, fluidic interconnections involve other types of fittings that allow the system integrator to assemble an air conditioning or refrigeration system, of which the MCHE is one component.

“Flux” refers to a chemical cleaning agent, flowing agent, or purifying agent, used in extractive metallurgy and metal joining. Fluxes may have more than one function in a particular application of use. As cleaning agents, fluxes facilitate soldering, brazing, and welding, by removing oxidation from the metals to be joined. In high temperature metal joining processes (e.g., welding, brazing, and soldering), flux prevents oxidation of the base and filler materials. Flux is typically inert at room temperature but at elevated temperatures, absorbs and prevents the formation of metal oxides. In metal joining processes, flux generally has the dual purpose of dissolving oxides on the metal surface and facilitating wetting of the molten metal, thereby acting as an oxygen barrier by coating the hot surface and preventing its oxidation.

“Fouling material” herein may include, but is not limited to, salts (such as, but not limited to, salt residue deposited from air in proximity to saltwater, such as sea air), bird excrement droppings, or other solid deposited material from the surrounding environment, or microbial (e.g., bacterial, fungal) material, such as a biofilm.

“Grain growth” refers to increase in size of grains (e.g., crystallites) in a material at high temperature. This occurs when recovery and recrystallization are complete and further reduction in internal energy is achieved by reducing the total area of grain boundary.

“Holdup liquid” refers to condensate or other liquid that is retained in the body of the heat exchanger that does not freely (e.g., via gravity or via the flow of air across the heat exchanger) leave the body of the heat exchanger.

“Hydrophilic” refers to a surface that has a high affinity for water. Contact angles can be very low (e.g. less than 30 degrees as measured from the surface through the liquid water in the presence of air) and/or immeasurable.

“Layered double hydroxide” refers a class of ionic solids characterized by a layered structure with the generic sequence [AcB Z AcB]_(n), where c represents layers of metal cations, A and B are layers of hydroxide anions, and Z are layers of other anions and/or neutral molecules (such as water). Layered double hydroxides are also described in PCT Application No. PCT/US2017/052120, which is incorporated by reference herein in its entirety.

A “macro void” refers to a geometric space within solid that has a characteristic dimension substantially larger than the characteristic dimension of an individual pore or feature (e.g., thickness), for example, at least about 5× to about 10× or about 10× to about 100× greater than the characteristic dimension.

“Mean” refers to the arithmetic mean or average.

“Mean pore diameter” is calculated using total surface area and total volume measurements from the Barrett-Joyner-Halenda (BJH) adsorption/desorption method as 4 times the total pore volume divided by the total surface area (4V/A), assuming a cylindrical pore.

“Multimodal” refers to a distribution which contains more than one different mode that appears as more than one distinct peak.

“Permeability” in fluid mechanics is a measure of the ability of a porous material to allow fluids to pass through it. The permeability of a medium is related to the porosity, but also to the shapes of the pores in the medium and their level of connectedness.

“Pore size distribution” refers to the relative abundance of each pore diameter or range or pore diameters as determined by mercury intrusion porosimetry (MIP) and Washburn's equation.

“Porosity” is a measure of the void (i.e., “empty”) spaces in a material, and is a fraction of the volume of voids, i.e., macro voids. over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Porosities disclosed herein were measured by mercury intrusion porosimetry.

“Porous” refers to spaces, holes, or voids within a solid material.

“Superhydrophobic” refers to a surface that is extremely difficult to wet. The contact angle of a water droplet on a superhydrophobic material here a superhydrophobic surface refers to a sessile drop contact angles >150°. Highly hydrophobic contact angles are >120°. Contact angles noted here are angles formed between the surface through the liquid.

“Surface area per square meter of projected substrate area” refers to the actual measured surface area, usually measured in square meters, divided to the surface area of the substrate if it were atomically smooth (no surface roughness), also typically in square meters.

“Thickness” refers to the length between the surface of the substrate and the top of the surface modification (e.g., ceramic) material.

“Third quartile pore diameter” refers to the value of the pore diameter at which the cumulative pore surface area determined in the direction of increasing pore size is equivalent to 75% of the total cumulative pore surface area as determined by BJH gas adsorption/desorption measurements.

“Tortuosity” refers to the fraction of the shortest pathway through a porous structure Δl and the Euclidean distance between the starting and end point of that pathway Δx.

“Tunable” refers to the ability of a function, characteristic, or quality of a material to be changed or modified.

EXEMPLARY EMBODIMENTS

Several exemplary but non-limiting embodiments and scenarios of heat exchanger processing are provided, referencing FIG. 1.

A. In one embodiment, the surface modification process (including a plurality of process steps) is conducted on site and prior to the application of the fluidic interconnections. The benefits of such an integration include reduced shipping, removal of cleaning requirements, and prevention of damage to fluidic interconnections. A surface coating is applied atop the heated flux material, which facilitates the brazing process.

A′. In another embodiment, the process is identical to A, with the exception that no flux is applied in process.

B. In another embodiment, the surface modification process (including a plurality of process steps) is conducted on site, immediately after the heat treatment step and prior to the application of the fluidic interconnections. The benefits of such an integration include the removal of surface preparation processing steps, reduced shipping, removal of cleaning requirements, and prevention of damage to fluidic interconnections. A surface coating is applied atop the heated flux material, which facilitates the brazing process. To be effective, the heat treatment and surface preparation steps should occur in a minimum of time (˜5 minutes, up to ˜12-24 hours) as determined by local ambient conditions. This time constraint would avoid surface fouling between steps, which could be facilitated by co-location or close geographic proximity of plants/processes.

C. In another embodiment, the surface modification process (including a plurality of process steps) is conducted on site and prior to heat treatment. The benefits of such an integration include the co-utilization of heating furnaces, reduced shipping, removal of cleaning requirements, and prevention of damage to fluidic interconnections. A surface coating is applied atop the flux prior to the brazing process. The surface modification may interact with the flux material in a conjoined heating process.

C′. In another embodiment, the surface modification process (including a plurality of process steps) is conducted on site and prior to heat treatment. The benefits of such an integration include the co-utilization of heating furnaces, reduced shipping, removal of cleaning requirements, removal of surface prep steps, and prevention of damage to fluidic interconnections. A surface coating is applied atop the flux prior to the brazing process. The flux serves in this capacity as a surface modifier, obviating the need for the surface preparation step (200).

C″ (not shown in FIG. 1). In another embodiment, the process is identical to C or C′, with the exception that secondary surface treatment (500) is not performed.

D. In another embodiment, the surface modification process (including a plurality of process steps) is conducted on site and prior to heat treatment. The benefits of such an integration include the co-utilization of heating furnaces, reduced shipping, removal of cleaning requirements, a co-curing of flux and surface modification materials to avoid damage due to shrinkage, and prevention of damage to fluidic interconnections. A surface coating is applied atop the flux prior to the brazing process. In this embodiment, the flux formulation is modified to preferentially remove aluminum oxides but not the surface modification material. The surface modification material interacts with the flux material to a lesser extent than certain other embodiments, for example, C, C′, or C″ as described above, or does not interact with the flux material in the conjoined heating process.

E. In another embodiment, no flux is used, and the surface modification material is applied to jigged parts with a common heat step, e.g., via ceramic bonding. Clad materials with no additional flux can be brazed, which would result in a ceramic bonding and brazing wherein the surface modification material is acting as a flux. The temperature for ceramic bonding processing is typically lower than the temperature that is required for brazing.

F. In another embodiment, no flux is used, and the surface modification material is applied to loose parts (pre jigged) with a common heat step.

G. In another embodiment, unclad parts are treated. Surface modification material is applied to loose or jigged (G′—not shown) parts. Flux (i.e., flux that interacts with surface modification material or flux that does not interact with surface modification material) is added after deposit of the surface modification material, with a common heat treatment. In this case, the surface modification material acts as the bonding agent (rather the existing cladded parts, solder, etc.)

H. In another embodiment, the process is identical to G, with the exception that no flux is added. The surface modification material serves as a bonding agent, and if necessary, also serves as a fluxing agent.

Structured Ceramic Materials

A coating or surface modification material as described herein may be a structured ceramic, for example, a binderless (e.g., surface immobilized) ceramic, such as a binderless ceramic with a crystallinity greater than about 20%. In some embodiments, the structured ceramic is porous. Nonlimiting examples of ceramic materials are provided in PCT/US19/65978, which is incorporated herein by reference in its entirety.

The ceramic material may include a metal oxide and/or hydroxide ceramic, for example, a single metal or mixed metal oxide and/or hydroxide ceramic. In some embodiments, the ceramic material includes a metal hydroxide and/or hydroxide ceramic, for example, a single metal or mixed metal oxide and/or hydroxide ceramic. In some embodiments, the ceramic material includes a metal oxide and a metal hydroxide ceramic, wherein the metal oxide and the metal hydroxide include the same or different single metal or mixed metal. In some embodiments, the ceramic material includes a metal oxide and/or a metal hydroxide ceramic, wherein the substrate is hydrated by water or other compounds resulting in a change of surface energy and potentially the ratio of metal oxide to metal hydroxide composition of the ceramic. In some embodiments, the ceramic material includes a metal hydroxide, wherein at least a portion of the metal hydroxide is in the form of a layered double hydroxide, e.g., at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% of the metal hydroxide is layered double hydroxide.

In some embodiments, a “metal oxide” or “metal hydroxide” may be in the form of a hydrate of a metal oxide or metal hydroxide, respectively, or a portion of the metal oxide or metal hydroxide may be in the form of a hydrate of a metal oxide or metal hydroxide, respectively.

A mixed metal oxide or mixed metal hydroxide may include, for example, oxides or hydroxides, respectively, of more than one metal, such as, but not limited to, iron, cobalt, nickel, copper, manganese, chromium, titanium, vanadium, zirconium, molybdenum, tantalum, zinc, lead, tin, tungsten, cerium, praseodymium, samarium, gadolinium, lanthanum, magnesium, aluminum, or calcium.

In some embodiments, the ceramic material is a binderless ceramic material, i.e., deposited onto a substrate without a binder. In some embodiments, the ceramic materials immobilized on the substrate.

In some embodiments, the ceramic material has an open cell porous structure, for example, characterized by one or more of: ability to effect capillary rise of a liquid having a low surface tension (e.g., less than about 25 mN/m, such as isopropanol) at greater than about 5 mm up a surface against gravity in a closed container in 1 hour; surface area of about 0.1 m²/g to about 10,000 m²/g; mean pore size of about 10 nm to about 1000 nm or about 1 nm to about 1000 nm; pore volume as measured by mercury (Hg) intrusion porosimetry of about 0 to about 1 cc/g; and tortuosity of about 1 to about 1000 as defined by the length of a fluid path to the shortest distance, the “arc-chord ratio”; and/or permeability of about 1 to about 10,000 millidarcy.

In some embodiments, the ceramic material is porous, with a porosity of about 5% to about 95%. In some embodiments, the porosity may be any of at least about or greater than about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%. In some embodiments, the porosity is about 10% to about 90%, about 30% to about 90%, about 40% to about 80%, or about 50% to about 70%.

In some embodiments, the porous ceramic material has a permeability of about 1 to 10,000 millidarcy. In some embodiments, the permeability may be any of at least about 1, 10, 100, 500, 1000, 5000, or 10,000 millidarcy. In some embodiments, the permeability is about 1 to about 100, about 50 to about 250, about 100 to about 500, about 250 to about 750, about 500 to about 1000, about 750 to about 2000, about 1000 to about 2500, about 2000 to about 5000, about 3000 to about 7500, about 5000 to about 10,000, about 1 to about 1000, about 1000 to about 5000, or about 5000 to about 10,000 millidarcy.

In some embodiments, the porous ceramic material includes a void volume of about 100 mm³/g to about 7500 mm³/g, as determined by mercury intrusion porosimetry. In some embodiments, the void volume is any of at least about 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, or 7500 mm³/g. In some embodiments, the void volume is any of about 100 to about 500, about 200 to about 1000, about 400 to about 800, about 500 to about 1000, about 800 to about 1500, about 1000 to about 2000, about 1500 to about 3000, about 2000 to about 5000, about 3000 to about 7500, about 250 to about 5000, about 350 to about 4000, about 400 to about 3000, about 250 to about 1000, about 250 to about 2500, about 2500 to about 5000, or about 500 to about 4000 mm³/g.

A porous ceramic material as disclosed herein may be characterized by its interaction with liquid materials. As previously noted, the ceramic material may be characterized the ability to effect capillary rise of a liquid having a low surface tension (e.g., less than about 25 mN/m, such as isopropanol) at greater than about 5 mm up a surface against gravity in a closed container in 1 hour. Other solvents with surface tension less than about 25 mN/m at 20° C. of may be used including, but not limited to, Perfluorohexane, Perfluoroheptane, Perfluorooctane, n-Hexane (HEX), Polydimethyl siloxane (Baysilone M5), tert-Butylchloride, n-Heptane, n-Octane (OCT), Isobutylchloride, Ethanol, Methanol, Isopropanol, 1-Chlorobutane, Isoamylchloride, Propanol, n-Decane (DEC), Ethylbromide, Methyl ethyl ketone (MEK), n-Undecane, Cyclohexane. Other solvents with surface tension at 20° C. of >25 mN/m may be used including: Acetone (2-Propanone), n-Dodecane (DDEC), Isovaleronitrile, Tetrahydrofuran (THF), Dichloromethane, n-Tetradecane (TDEC), sym-Tetrachloromethane, n-Hexadecane (HDEC), Chloroform, 1-Octanol, Butyronitrile, p-Cymene, Isopropylbenzene, Toluene, Dipropylene glycol monomethylether, 1-Decanol, Ethylene glycol monoethyl ether (Ethyl Cellosolve), 1,3,5-Trimethylbenzene (Mesitylene), Benzene, m-Xylene, n-Propylbenzene, Ethylbenzene, n-Butylbenzene, 1-nitro propane, o-Xylene, Dodecyl benzene, Fumaric acid diethylester, Decalin, Nitroethane, Carbon disulfide, Cyclopentanol, 1,4-Dioxane, 1,2-Dichloro ethane, Chloro benzene, Dipropylene glycol, Cyclohexanol, Hexachlorobutadiene, Bromobenzene, Pyrrol (PY), N,N-dimethyl acetamide (DMA), Nitromethane, Phthalic acid diethylester, N,N-dimethyl formamide (DMF), Pyridine, Methyl naphthalene, Benzylalcohol, Anthranilic acid ethylester, Iodobenzene, N-methyl-2-pyrrolidone, Tricresylphosphate (TCP), m-Nitrotoluene, Bromoform, o-Nitrotoluene, Phenylisothiocyanate, a-Chloronaphthalene, Furfural (2-Furaldehyde), Quinoline, 1,5-Pentanediol, Aniline(AN), Polyethylene glycol 200 (PEG), Anthranilic acid methylester, Nitrobenzene, a-Bromonaphthalene (BN), Diethylene glycol (DEG), 1,2,3-Tribromo propane, Benzylbenzoate (BNBZ), 1,3-Diiodopropane, 3-Pyridylcarbinol (PYC), Ethylene glycol (EG), 2-Aminoethanol, sym-Tetrabromoethane, Diiodomethane (DI), Thiodiglycol (2,2′-Thiobisethanol) (TDG), Formamide (FA), Glycerol (GLY), Water (WA), and Mercury

The porous ceramic surface modification material may possess the ability to effect capillary rise of water, at various temperatures. These materials may have the ability to separate miscible materials and binary azeotropes, such as ethanol-water, ethyl acetate-ethanol, or butanol-water, to break ternary azeotropes, or to remove amyl alcohol from mixtures including ethanol and water.

The pores of the porous ceramic surface modification material may include open cells filled with one or more gas, may include partially filled cells (e.g., partially filled with one or more solid material(s)), or may include completely or substantially filled cells (e.g., completely or substantially filled with one or more liquid and/or solid material(s)). In some embodiments, the pores are partially, substantially, or completely filled with a gas, liquid, or solid substance, or combinations thereof.

In some embodiments, the pores are partially filled with a first material and then partially or completely filled with a second material. In some embodiments, the second material is added as a layer of material over partially filled pores. In some embodiments, the first material is a gas, solid, or liquid, or combination of gas, liquid, and/or solid substance(s). In some embodiments, the second material is a gas, solid, and/or liquid substance(s), or the environment (e.g., air). Examples include, and functions thereby imparted include changes in the porosity, wicking, repellency and/or wetting behavior; changes in the composite (comprising the porous material and second material) to modify electrical/dielectric properties, to modify mechanical properties such as abrasion resistance, hardness, toughness, tactile feel, elastic modulus, yield strength, yield stress, Young's modulus, surface (compressive or tensile) stress, and/or elasticity; changes in thermal properties such as thermal diffusivity, conductivity, thermal expansion coefficient, thermal interface stress, and/or thermal anisotropy; modification of optical properties such as emissivity, color, reflectivity, and/or absorption coefficients; modification of chemical properties such as corrosion, catalysis, reactivity, inertness, compatibility, fouling resistance, ion pump blocking, microbial resistance, and/or microbial compatibility; and/or as a substrate for biocatalysis.

In some embodiments, the first material interacts with the second material in a positive or negative synergistic manner to alter one or more functional characteristic of the ceramic material, such as, but not limited to, wettability, hardness, elasticity, a mechanical, electrical, piezoelectric, optical, adhesion, or thermal property, microbial affinity or resistance, alteration of biofilm growth, catalytic activity, permeability, aesthetic appearance, liquid repellency, and/or corrosion resistance.

Nonlimiting materials that may be used to partially or completely fill pores include molecules capable of binding to the surface such as molecules with a head group and a tail group wherein the head group is a silane, phosphonate or phosphonic acid, a carboxylic acid, vinyl, a hydroxide, a thiol, or ammonium compound. The tail group can include any functional group such as hydrocarbons, fluorocarbons, vinyl groups, phenyl groups, and/or quaternary ammonium groups. Other ceramic materials can also be deposited into the pores partially or completely. Polymers may also be deposited into the pores partially or completely. Ceramic materials may include, for example, one or more oxide of zinc, aluminum, manganese, magnesium, cerium, gadolinium, and cobalt. In addition, ceramic materials may include any solid material which can be added to the surface modification material, including an inorganic compound of metal, non-metal, or metalloid atoms primarily held in ionic and covalent bonds, such as, for example, clays, silicas, and glasses. Polymers may include, for example, natural polymeric materials such as hemp, shellac, amber, wool, silk, natural rubber, cellulose, and other natural fibers, sugars, hemi- and holo-celluloses, polysaccharides, and biologically derived materials such as extracellular proteins, DNA, chitin. Synthetic polymers include, for example, polymers and co-polymers containing polyethylene, polypropylene, polystyrene, polyvinyl chloride, synthetic rubber, phenol formaldehyde resin(or Bakelite), neoprene, nylon, polyacrylonitrile, PVB, silicone, polyisobutylene, PEEK, PMMA, and PTFE.

In some embodiments, the pores are filled partially with a thin composite polymer layer to produce a surface modification material that has porosity and functionality provided by the polymer. In other embodiments, the pores are filled completely with a thick polymer layer to produce a surface modification material with a thick polymer layer that has composite properties of the porous base material and the polymer layer. A polymer as described in the compositions herein includes co-polymers.

In some embodiments, the pores are partially or completely filled with a layer of material deposited over the surface of the surface modification material. In some embodiments, a layer of material is deposited that adds one or more functional group(s) to the surface modification material, such as, but not limited to, ammonium groups (e.g., quaternary ammonium groups), alkyl groups, perfluoroalkyl groups, fluoroalkyl groups. In some embodiments, a polymer or ceramic layer is deposited. In one embodiment, a ceramic top surface layer is deposited which is the same or different ceramic than the ceramic of the binderless porous ceramic material on the substrate. Examples of functional group(s) and functions thereby imparted include quaternary ammonium groups for anti-microbial functions, alkyl chains for water repellency and hydrocarbon affinity, perfluoroalkyl groups for water and oil repellant functions, polymers for mechanical property function, other ceramics for aesthetic functions, optoelectronic functions, or anti-corrosive functions.

In some embodiments, the pores are partially or completely filled with a gas, liquid, or solid substance, or combinations thereof, and the composition further includes a layer of a top surface material over the ceramic material, and the top surface material imparts one or more functionality, such as, but not limited to, wettability with a liquid and/or selective separation of compounds in a liquid. In certain embodiments, the top surface material is a separate material from the substance with which the pores are partially, substantially, or completely filled, and does not itself fill or intrude into the pores. In some embodiments, the top surface material interacts with the substance(s) in the pores. For example, the top surface material may interact with the substance(s) in the pores to provide one or more functionality, such as, but not limited to, thermal management, electrochemical reactivity modulation, and/or mechanical property modulation. In certain embodiments, the top surface material is the surrounding environment with which the binderless porous ceramic material is in contact.

In some embodiments, the pores are substantially or completely filled with a polymer or with a ceramic material.

In some embodiments, a material in the pores interacts with the ceramic material. Examples of such materials and functions thereby imparted include the oxidation of the surface modification material by ambient liquid or vapor, the condensation of minor components (e.g., environmental pollutants), the capture or oxidation of hazardous environmental materials such as CO or H₂S from environmental air, and/or the collection and retention of materials in the environment.

In some embodiments, moisture in the environment or added to the pores interacts with a material in the pores to modify the material in the pores or the surface modification material. Examples of such materials and functions thereby imparted include changes in wetting behavior, in optical properties, changes in oxidation state or reactivity, changes in the rate of evaporation, frosting, icing, or condensation.

In some embodiments, material in the pores may be designed to interact with the ceramic material to “tune” the properties of the overall surface. Examples of tunable properties includes, but are not limited to, wettability, hardness, microbial resistance, catalytic activity, corrosion resistance, color, and/or photochemical activity.

In some embodiments, the ceramic surface modification material and a material in the pores interact in a synergistic manner, for example, enhancing or reducing at least one functionality of the surface modification material and/or the material in the pores, in comparison to the functionality of the surface modification material and/or the material in the pores alone. In some embodiments, two or more materials in the pores interact in a synergistic manner, for example, enhancing or reducing at least one functionality of at least one material in the pores, in comparison to the functionality of that material alone.

In some embodiments, the ceramic surface modification material is asymmetric, for example, a pore morphology that is not spherical, cylindrical, cubic or otherwise ordered as having a well-defined, relatively constant, normal distribution of surface area to volume, as characterized a by a ratio of the pore diameter at the first quartile to the pore size at the third quartile as a function of the thickness of the binderless ceramic surface modification. In particular, the pore morphology is asymmetric about its center when compared to a spherical, cylindrical, or cubic structure. A nonlimiting example of asymmetric pores is depicted in PCT Application No. PCT/US19/39743, which is incorporated by reference herein in its entirety.

A porous ceramic surface modification material may be characterized by a broad pore size distribution that varies with distance from the substrate. In particular, the pore structure at a given distance from the substrate can be characterized locally, e.g., as described herein and has a different characterization at a different distance. The resulting asymmetry is determined in situ by the combination of substrate, ionic mobility, processing conditions such as temperature, pressure, and concentrations. The degree of asymmetry can be further modified through bulk means such as mixing, agitation, electric field modulation, and tank filtration, or through surface directed process means such as shear rates, impinging flows or surface charge modification and modulation. The asymmetry can be determined ex situ through a variety of means such as etching, track etching, ion beam milling, oxidation, photocatalysis, or through additional means. These approaches are to refer to materials which have a narrower, or symmetric pore structures, with thickness and/or pore depth, such as zeolites, track etched membranes, or expanded PTFE membranes.

In some embodiments, the porous ceramic surface modification material includes mesoporous mean pore sizes that range from about 2 nm to about 50 nm. In other embodiments, the mean pore sizes range from about 50 nm to about 1000 nm. In some embodiments, the binderless porous ceramic material includes a mean pore diameter of about 2 nm to about 20 nm. In some embodiments, the mean pore diameter is any of at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nm. In some embodiments, the mean pore diameter is any of about 2 to about 5, about 4 to about 9, about 5 to about 10, about 7 to about 12, about 9 to about 15, about 12 to about 18, about 15 to about 20, about 4 to about 11, about 5 to about 9, about 4 to about 8, or about 7 to about 11 nm.

The ceramic surface modification material may include one or more metal oxide and/or metal hydroxide (and/or hydrates thereof). Non-limiting examples of metals that may be included in the ceramic compositions disclosed herein include: zinc, aluminum, manganese, magnesium, cerium, copper, gadolinium, tungsten, tin, lead, and cobalt. In some embodiments, the ceramic material includes a transition metal, a Group II element, a rare-earth element (e.g., lanthanum, cerium gadolinium, praseodymium, scandium, yttrium, samarium, or neodymium), aluminum, tin, or lead. In some embodiments, the ceramic material includes two or more metal oxides (e.g., a mixed metal oxide) including but not limited to zinc, aluminum, manganese, magnesium, cerium, praseodymium, and cobalt.

In some embodiments, the ceramic surface modification material includes: a mixture of zinc and aluminum oxides and/or hydroxides; a mixture of ZnO and Al₂O₃, and Zn-aluminates; mixtures of materials comprising any/all phases comprising Zn, Al, and oxygen; a mixture of manganese and magnesium oxides and/or hydroxides; manganese oxide; aluminum oxide; a mixed metal manganese oxide and/or hydroxide; a mixture of magnesium and aluminum oxides and/or hydroxides; a mixture of magnesium, cerium, and aluminum oxides and/or hydroxides; a mixture of zinc, gadolinium, and aluminum oxides and/or hydroxides; a mixture of cobalt and aluminum oxides and/or hydroxides; a mixture of manganese and aluminum oxides and/or hydroxides; a mixture of cerium and aluminum oxides and/or hydroxides; a mixture of iron and aluminum oxides and/or hydroxides; a mixture of tungsten and aluminum oxides and/or hydroxides; a mixture of tin and aluminum oxides; tungsten oxide and/or hydroxide; magnesium oxide and/or hydroxide; manganese oxide and/or hydroxide; tin oxide and/or hydroxide; or zinc oxide and/or hydroxide.

In some embodiments, at least one metal in the ceramic material is in the 2⁺ oxidation state.

In some embodiments, the ceramic surface modification material includes one or more oxide and/or hydroxide of zinc, aluminum, manganese, magnesium, cerium, gadolinium, and cobalt, and the substrate is aluminum or an aluminum alloy.

In some embodiments, the ceramic surface modification material is superhydrophobic. In some embodiments, the surface modification material is highly hydrophobic. In some embodiments, the surface modification material includes one or more functional characteristic selected from wettability, hardness, elasticity, mechanical, electrical, piezoelectric, electromagnetic, optical, adhesion, or thermal properties, microbial affinity or resistance, alteration of biofilm growth, catalytic activity, permeability, aesthetic appearance, and corrosion resistance, in comparison to a substrate that does not include the ceramic material.

In some embodiments, a functional material layer (e.g., top layer of material) is deposited onto the ceramic material. Examples of such materials include, but are not limited to, quaternary ammonium groups for anti-microbial functions, alkyl chains for water repellency and hydrocarbon affinity, perfluoroalkyl groups for water and oil repellant functions, polymers for mechanical property function, other ceramics for aesthetic functions, optoelectronic functions, or anti-corrosive functions. Examples of functionalities imparted by such materials include, but are not limited to, changes in the porosity, wicking, repellency, and/or wetting behavior; changes in the composite (including the porous material and second material) to modify electrical/dielectric properties, to modify mechanical properties such as abrasion resistance, hardness, toughness, tactile feel, elastic modulus, yield strength, yield stress, Young's modulus, surface (compressive or tensile) stress, tensile strength, compression strength, and/or elasticity; thermal properties such as thermal diffusivity, conductivity, thermal expansion coefficient, thermal interface stress, thermal anisotropy, to modify optical properties such as emissivity, color, reflectivity, and/or absorption coefficients, to modify of chemical properties such as corrosion, catalysis, reactivity, inertness, compatibility, fouling resistance, ion pump blocking, microbial resistance and/or microbial compatibility, promotion of adhesion of subsequent material layers, and/or as a substrate for biocatalysis.

In some embodiments, the ceramic surface modification material is resistant to degradation by ultraviolet radiation, in comparison to the substrate material, such as a polymer or any of the substrate materials disclosed herein.

In some embodiments, the ceramic surface modification material includes a thickness of about 0.5 micrometers to about 20 micrometers. In some embodiments, the ceramic material includes a thickness of about 0.2 micrometers to about 25 micrometers. In some embodiments, the thickness is any of at least about 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25 micrometers. In some embodiments, the thickness is any of about 0.2 to about 0.5, about 0.5 to about 1, about 1 to about 5, about 3 to about 7, about 5 to about 10, about 7 to about 15, about 10 to about 15, about 12 to about 18, about 15 to about 20, about 18 to about 25, about 0.5 to about 15, about 2 to about 10, about 1 to about 10, about 3 to about 13, about 0.5 to about 15, about 0.5 to about 5, about 0.5 to about 10, or about 5 to about 15 micrometers.

In some embodiments, the ceramic surface modification material is characterized by a water contact angle of about 0° to about 180°. In other embodiments, the water contact angle is less than about 30 degrees. In other embodiments the water contact angle is greater than about 150 degrees.

In some embodiments, the ceramic surface modification material includes a surface area of about 1.1 m² to about 100 m² per square meter of projected substrate area. In some embodiments, the ceramic material includes a surface area of about 10 m² to about 1500 m² per square meter of projected substrate area. In some embodiments, the surface area is any of at least about 10, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, or 1500 m² per square meter of projected substrate area. In some embodiments, the surface area is any of about 10 to about 100, about 50 to about 250, about 150 to about 500, about 250 to about 750, about 500 to about 1000, about 750 to about 1200, about 1000 to about 1500, about 70 to about 1000, about 150 to about 800, about 500 to about 900, or about 500 to about 1000 m² per square meter of projected substrate area.

In some embodiments, the ceramic material includes a surface area of about 15 m² to about 1500 m² per gram of ceramic material. In some embodiments, the surface area is any of at least about 15, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450, or 1500 m² per gram of ceramic material. In some embodiments, the surface area is any of about 15 to about 100, about 50 to about 250, about 150 to about 500, about 250 to about 750, about 500 to about 1000, about 750 to about 1200, about 1000 to about 1500, about 50 to about 700, about 75 to about 600, about 150 to about 650, or about 250 to about 700 m² per gram of ceramic material.

Substrates

The substrate (e.g., heat exchanger component) on which one or more coating or surface modification materials as described herein are applied or deposited may be composed of any material suitable for the structural or functional characteristics, or functional application of use, for example, in a device, such as a heat exchanger. In some embodiments, the substrate is aluminum or contains aluminum (e.g., an aluminum alloy), a ferrous alloy, zinc, a zinc alloy, copper, a copper alloy, a nickel alloy, nickel, a titanium alloy, titanium, a cobalt-chromium containing alloy, glass, a polymer, a co-polymer, a natural material (e.g., a natural material containing cellulose), or a plastic.

In some embodiments, the substrate includes a metal, and the primary metal in a ceramic surface modification material as described herein is different than the primary metal in the substrate. A primary metal is a metal that is at least about 50%, 60%, 70%, 80%, 90%, or 95% of the total metal in the substrate or the ceramic material, e.g., as determined by x-ray diffraction on an atomic metals basis. Examples of substrate primary metals include, but are not limited to, aluminum, iron, copper, zinc, nickel, titanium, and magnesium. Examples of ceramic primary metals include, but are not limited to, zinc, aluminum, manganese, magnesium, cerium, copper, gadolinium, tungsten, tin, lead, and cobalt.

In some embodiments, the substrate includes a metal that is able to react (e.g., dissolve) under reaction conditions that allow for local dissolution of the substrate metal, and the substrate metal is incorporated into a substrate modification material, such as a ceramic material, e.g., a binderless porous ceramic material. For example, an aluminum substrate may provide aluminum (e.g., Al²⁺) that is incorporated into ceramic material as the ceramic material is deposited on the substrate.

In some embodiments, the substrate includes more than one class or type of materials, such as a metal and a polymer joined by ceramics as described herein, a metal and a ceramic joined by ceramics as described herein, a polymer and a ceramic joined by ceramics as described herein, or substrates of more than two different types of materials joined by ceramics as described herein.

Selective Coating of Surface Modification Materials

In certain embodiments, selective application of coating compositions (surface modification materials) as described herein can be used to provide protection against environmental damage. Furthermore, over time, the conditions to be prevented or treated change, which can be addressed through a layered coating structure which provides different protections as the layers are altered, for example, through the lifetime of a device.

Provided herein are coating compositions and substrate modifications to minimize environmental wear or degradation, such as corrosion, in areas where environmental exposure and damage is especially challenging, such as on edges, material or composite interfaces, regions of regions of low velocity, regions of high electrochemical corrosion potential, or that are exposed to or susceptible to excess moisture, salt, debris accumulation, biofouling, or abrasion.

Coating materials or surface modification may be used to apply more corrosion resistant materials or to promote or enhance movement of a liquid, such as water, away from a substrate, in areas of high environmental exposure or stress, or stress due to operational factors during usage of a device or system as described herein, to partially coat a component in instances where coating of an entire surface or device is not needed, to protect materials differently over time, e.g., through differences in thickness of coating material or surface modification across a substrate surface or through a surface normal gradient (for example, a gradient of one or more chemical or physical property from the top of the coating material or surface modification to the bottom which is in contact with the substrate surface) and/or as a branding or cost cutting measure.

Selective application of coating materials or surface modifications can also be used achieve complementary benefit such as corrosion resistance while minimizing potential negative impacts such as heat transfer losses due to thermal resistance of the coating.

Some outdoor heat exchangers corrode and fail at very specific locations due to standing water after a rain, sprinklers, proximity to or use in marine environments, or animal, e.g., cat, urination. Other environmental stresses that may be mitigated or eliminated by application of the compositions and surface modifications described herein include exhaust pollution, urban pollution, dust/debris, fertilizer, road salt, sand, marine aerosols, industrial emissions (e.g., refinery, water treatment, manufacturing), or microbial, bacterial, fungal, or viral exposure and/or degradation, including biofilm formation (i.e., anti-microbial, anti-bacterial, anti-fungal, or anti-viral coating or surface modification). Spatial gradients of properties can be used to create a gradient effect. For example, a spatial gradient of porosity that directionally wicks a fluid such as water and “pumps” it from one direction to another may be used for anti-corrosion and other purposes, such as enhanced drying or fluid transfer.

In some embodiments, the coating or surface modification may render a heat exchanger or component thereof, or a component of a system as described herein, resistant to impinging pollutants (e.g., slaughterhouse particles, corrosive aerosols, etc.) and increase thermal resistance to decrease frosting rate, by reducing thermal conductivity and thereby increasing surface temperature. Downstream in the fin pack, the coating may be different to reduce corrosion resistance rate and improve heat transfer/frost suppression properties.

A coating or surface modification may be applied to an entire substrate surface or selectively (to one or more portion of a substrate surface, such as to one or more area that is exposed to adverse environmental conditions or subject to environmental or operational stress). In certain embodiments described herein, coating or surface modifications are configured as a gradient i.e., spatial variability) in one or more dimension, across a substrate surface or across a device or a portion or component of a device. Exemplar material parameters may include gradients in material density, pore size distribution, pore i.e., fraction, or spatial gradient of a materials filling pores of a porous material), or material thickness.

The selective coating of a substrate, such as a surface of a heat exchanger or microchannel coil, can be performed in multiple ways, such as: partial (selective) coating on a portion of the surface of a substrate, where some locations are uncoated and some are coated, based on local corrosion resistance need or other needs, such as, but not limited to, limiting microbial growth in regions of high moisture (e.g. Legionella) or movement of a liquid, such as water, away from the substrate; complete coating of a substrate with first material A and partial coating of a second material B over the first material (i.e., selective coating of second material B over a portion (one or more areas) of the surface of first material A), where the second material may be the same as or different from the first material; and a gradient within a coating across the substrate based on need for protection from environmental or operational stress conditions.

A gradient may be spatially variable with respect to at least one chemical or physical property. For example, a coating or surface modification material A may be a uniform material on a substrate surface or may include a spatial gradient (variability) in one or more property such as, but not limited to, material density, pore size distribution, pore filling fraction, or thickness. Additionally, an optional second material B may also be applied over material A, which may be a uniform material or may possess spatial variability in one or more property, such as, but not limited to, material density, pore size distribution, thickness, and/or filling fraction of the pores of material A. In some embodiments, an optional third material C may also be selectively applied and may be a uniform material across the substrate or across the material directly below or may possess spatial variability in one or more property, such as, but not limited to, material density, pore size distribution, thickness, and/or filling fraction of the pores of material B. In some embodiments, material C is applied over a stack of materials, such as, but not limited to, A-B-A, and may possess spatial variability in one or more property, such as, but not limited to, material density, pore size distribution, thickness, and/or filling fraction of the pores of the material directly below material C, e.g., material A. Additional optional layers of uniform or gradient materials may also be included. The coating or surface modification material(s) may be applied continuously across the substrate surface or in one or more discrete (selective) areas, such as areas of the substrate that are subject to environmental or operational stress in an application of use for a device or component into which the substrate is incorporated.

A gradient layer may include a gradient of one or more property of a structural layer. For example, a gradient may include higher porosity near a joint, a change in structural composite thickness on a panel, e.g., thicker near the bottom or edges from the draining and dryout of an immersion process at a specific temperature, selectively spraying materials in select regions, adding additional coats of materials in select regions, configuration of spray application resulting in a greater addition of material at the leading edge, or a composition change impacting electrochemical potential.

A gradient may be developed during processing of a structural layer, for example, by changing concentration levels (dropping) during processing, which results in changes in the composition through the thickness of the coating, and/or changing temperature during processing bath to change structure or to change part temperature either during processing, or having a hot zone and a cold zone of the part to result in thicker, thinner, or different materials, e.g., structural ceramic materials. Modification of the local chemical reactivity through mechanical part agitation, fluid advection, addition of localized heat or light, pressure differences and/or gravitational settling differences can also be used to generate gradient properties. The drying and curing process can also be used to generate property gradients through the use of select temperature zones, drying orientations, and selective light addition.

In some embodiments, one or more coating or surface modification material (e.g., materials A-C) is a structured ceramic, such as a binderless ceramic surface modification material, for example, with pores that may be filled, unfilled, or partially filled, optionally in a manner that produces a gradient with respect to partial filling of the pores with a second material. In one embodiment, the ceramic material includes a contiguous network of pores filled with a second material, such as a polymer material.

In some embodiments, one or more surface modification material is a monolayer chemistry, which may provide any of an array of properties, such as, but not limited to, wettability, sealant, optical, etc.

Many heat exchangers have multimetal components (e.g., a composite interface), such as copper-aluminum heat exchangers, steel-aluminum heat exchangers, and brazed aluminum heat exchangers. Selective protection in these composite scenarios can provide additional protection for galvanic corrosion susceptible metal couples (e.g. selective anode protection) for a wide variety of environments and anodic/cathodic areas. The methods described herein may also be applied to introduce electrically insulating materials or to disrupt galvanic cell formation. Other substrates, homogenous or heterogenous in composition, contain local areas susceptible to corrosion due to local environments such as local abrasion, standing liquids, or air flow gradients, which may be mitigated by selective surface modification as described herein.

The following examples are intended to illustrate, but not limit, the invention.

EXAMPLES

Surface modification materials on a substrate (e.g., heat exchanger component) were prepared according to the following general procedure. The substrate assemblies were spot cleaned with isopropanol to remove any residual oils. Next, the parts were submerged in an alkali metal caustic etch bath at pH>11 at a temperature from about 20° C. to about 60° C. for about 5 minutes to about 20 minutes. The assemblies were then rinsed in distilled or deionized water to remove any residual caustic or loosely adhered material. Next, the parts were submerged in a non-coordinating oxidizing acid (such as nitric acid) solution with pH below 2 and temperature of about 20° C. to about 60° C. to remove the smut and/or deoxidize the substrate. The assemblies were then placed into the production bath containing 20-250 mM of metal nitrate (such as manganese (II) nitrate) or sulfates (such as manganese (II) sulfate) or mixed metal nitrates (such as manganese (II) nitrate and zinc nitrate, typically in a ratio from about 50:1 to about 1:50) or sulfates and a similar molar amount of a diamine (such as urea or ethylenediamine), triamine, or tetraamine (such as hexamethylenetetramine), typically in a ratio from about 2:1 to about 0.5:1, that were heated to a reaction temperature of about 50° C.-85° C. The assemblies were maintained in the bath for times ranging from about 5 minutes to about 3 hours. The assemblies were removed, rinsed in distilled or deionized water, and placed into an oven to dry and/or calcine at 50-600° C. for several minutes to several hours. This deposit step can optionally be repeated (with the same or different metal salt) before or after the drying step followed by another optional drying step, if desired. In some embodiments, the metal in the deposited coating can come from the substrate (such as the aluminum in the deposit comprising zinc and aluminum hydroxides/oxides). After cooling, the parts were further processed and/or tested as described in the examples below.

Example 1 Coated Heat Exchanger, No Cleaning

A microchannel heat exchanger was manufactured by taking loose parts, and assembling them together. The assembled parts were sprayed with brazing flux, with the excess removed, and heated in a controlled atmospheric brazing furnace. The brazed heat exchanger, after an initial processing in the brazing furnace, was processed without cleaning. Typically, regions of surfaces subject to aqueous processing which debris or oil result in a region of nonuniformity as observed by nonuniform wetting behavior. In practice, this is termed a water break test and a standard test method (ASTM F22) is available. The heat exchanger was uniform and was processed directly in surface prep, deposit, thermal treatment, deposit treatment and surface finishing. The uniformity and resulting surface treatment was uniform and conformal as noted by water break tests. This example corresponds to a nonlimiting example of case A of FIG. 1.

Example 2 Coated Heat Exchanger, No Cleaning or Surface Preparation

A microchannel heat exchanger was manufactured by taking loose parts, and assembling them together. The assembled parts were sprayed with brazing flux, with the excess removed, and heated in a controlled atmospheric brazing furnace. The brazed heat exchanger, after an initial processing in the brazing furnace, was processed without cleaning. Typically, regions of surfaces subject to aqueous processing which debris or oil result in a region of nonuniformity as observed by nonuniform wetting behavior. In practice, this is termed a water break test and a standard test method (ASTM F22) is available. The heat exchanger was uniform and was processed directly in deposit, thermal treatment, deposit treatment and surface finishing. Successful coatings require the substrate to have low and uniform surface energy. In this case, the thermal processing of the brazing furnace resulted in a uniform surface, which resulted in a uniform coating. The time between heat exchanger brazing surface preparation processing was 84 hours. The uniformity and resulting surface treatment was uniform and conformal as noted by water break tests. This example corresponds to a nonlimiting example of case B of FIG. 1.

Example 3 Ceramic Bonding (Tubes)

A 0.5 inch 6061-T6 ring was placed onto a 0.5 inch OD 6061-T6 aluminum tube secured firmly with a 18-8 stainless steel set screw. There was an estimated gap between the ring and tube of 0.005 inches. This assembly was then etched in an aqueous sodium hydroxide solution to clean the surface, and desmutted in a nitric acid-water solution. The assembly was then placed into a warm water bath containing a 2⁺ metal anionic salt for several hours. The resulting part was then baked to remove water and organic components for a period of 24 hours. Surprisingly, upon removal from the drying step, the ring was impossible to remove from the tube with bare hands or hand tools. The process resulted in material filling the gap resulting in a very strong ceramic bond between the ring and the tube. This example corresponds to a nonlimiting example of cases E, F, and H of FIG. 1.

Example 4 Ceramic Bonding—Loose Parts Versus Jigged Parts

Sections of 1 inch (in.) diameter aluminum alloy manifold tube 4 in. long (predrilled) and 6 in. long sections of microchannel tubes were tested. In one case, the microchannel was bent into a U shape, and inserted into the manifold. In the other case, the microchannel tubes and manifold tubes were treated independently. The assembly and the loose parts were treated with alkaline etching, followed by an acid treatment step. Following this surface treatment, the components were subject to a surface treatment by placing them into a warm water bath containing a 2⁺ metal anionic salt for just over one hour. The loose parts were then assembled by placing the microchannel into the manifold. The two assemblies were then baked to remove water and organic components for a period of 4 hours.

Both assemblies looked uniform and were subject to mechanical testing. The estimated contact area at each joint of the microchannel and manifold is 0.15 in². The manifold assemblies were mounted with the microchannel joint hanging below the manifold. Weights were added to the microchannel to determine the weight that caused the microchannel to separate from the manifold. The preassembled assembly withstood a weight of 65 pounds (lbs) before separating. The separate parts, after assembly and treatment, withstood a weight of 55 lbs before separating. This example corresponds to a nonlimiting example of cases E, F, and H of FIG. 1.

Example 5

A microchannel heat exchanger was manufactured by taking loose parts, and assembling them together. The assembled parts were sprayed with brazing flux, the excess was removed, and the parts were then heated in a controlled atmospheric brazing furnace. The brazed heat exchanger, after an initial processing in the brazing furnace, was processed without cleaning. Typically, regions of surfaces subject to aqueous processing which debris or oil result in a region of nonuniformity as observed by nonuniform wetting behavior. In practice, this is termed a water break test and a standard test method (ASTM F22) is available. The surface of the heat exchanger was uniform and was processed by prepping the surface with an alkaline process step, followed by an acid treatment to reduce the surface concentration of metals other than aluminum. After surface preparation, the heat exchanger was subjected to a deposit step, thermal treatment, deposit treatment and surface finishing. The contact angle, as a measure of surface modification performance, was measured at various points of the process. Of note, the contact angle was measured at various points in the process on both the substrate and on regions of excess brazing flux. The results are below in Table 1. This example corresponds to a nonlimiting example of case A of FIG. 1.

TABLE 1 Contact angle on Contact angle on base material excess flux As received, prior to surface ~60° ~50° preparation After surface preparation, <20° <20° deposit and deposit thermal treatment After deposit treatment and >165°  >165°  surface finishing

Example 6

The ability of surface modification materials, as described herein, to provide a self-cleaning function, reducing the amount of debris and fouling materials on a modified surface, was investigated. A fine cardboard lint was applied to 3 in.×3 in. samples of coated and uncoated aluminum. A small hand spray bottle filled with water was used to spray water on the samples which were mounted side by side in orientation of 10° to the vertical.

The results are shown in FIG. 2. There are two plates, side by side, one uncoated and one coated. The image on the upper left is time zero. Then the images go in sequence from top to bottom.

In the first image, cardboard lint can be seen inside the black oval. It was observed that the cardboard lint was readily removed from the coated sample and very little water was retained on the surface.

In image no. 8, on the uncoated side, water droplets containing the lint were observed to adhere to the substrate (white square). The cardboard lint was not readily removed from the substrate.

The contact angle of the coating was >120°.

Example 7

A refrigeration system was constructed that included a ¼ hp R-134 condensing unit, a needle valve to control the throttling process, and a small microchannel heat exchanger with face area of approximately 200 mm×100 mm and with a depth of approximately 25 mm, and was mounted into a plexiglass wind tunnel. The wind tunnel contained a fan which pulled air through the coil at velocities from 1-5 m/s, cooling the air and generating condensate in situations in which the coil temperature was below the dew point of the room. Inlet air was from an air conditioned room of ˜1000 ft², with temperatures that ranged from 18-20° C. and the relative humidity ranged from 40-50%. The system was designed in such a way that the system could be evacuated, the coil isolated from the remainder of the system, the coil replaced, and the system recharged with R-134. In addition to visual observations, pressure drop across the coil and refrigerant pressures were monitored throughout the system.

The refrigerant coils included a refrigerant inlet distribution manifold, a series of vertically oriented microchannel tubes, and a series of fins that spanned the space between individual tubes and a refrigerant outlet manifold. Several microchannel coil configurations were tested, with two different louver configurations: (a) unlouvered—solid fins; and (b) louvered fins to increase the heat transfer efficiency of air to the heat exchanger, and two different coating configurations: (1) as received from the manufacturing process; and (2) coated with a surface modification material as described herein, and a fluorinated top coat.

The testing protocol consisted of mounting a new coil and charging the system with refrigerant. The metering valve was closed to avoid any refrigerant flow. The fan was turned on to set the flow velocity and initial pressure drop across the dry coil. The pressure drop for the (b) louvered coils was approximately 20% greater than the (a) unlouvered coils in a dry condition. There was no significant difference in pressure drop for (2) coated coils vs (1) coils in an as manufactured configuration.

The refrigerant pressures were controlled through the metering valve and the condensing unit compressor. The high side pressures were 90-110 psig and the inlet evaporator pressure was adjusted to around 30 psig which corresponds to a refrigerant temperature of about 1.1° C. The pressure drop in the refrigerant across the coils ranged from 1-1.5 psig. During testing, evaporator inlet pressures were adjusted from 30-24 psig resulting in refrigerant temperatures of 1.1 to −3.8° C. These conditions generated condensate on the coil under these conditions. The condensate generated in the (2) coated coils was observed to be more greatly retained at the trailing edge than the (1) uncoated coils. It appears that the (2) coated coils generated a greater amount of condensate, however the collection of all condensate from each test condition was uncertain due to retention of some condensate in the coils (as indicated by increased pressure drop across the coils of 0-5 Pa during testing), some drainage from the manifold exterior, some condensate in the tunnel, and some condensate passing to the fan. Both the (2) coated coils and the (1) uncoated coils were observed to remove significant condensate from the ambient air, indicating effective heat transfer and thus dehumidification, conditioning the air. Each test condition was run for ˜120 minutes to ensure a steady state was reached.

Although the foregoing invention has been described in some detail by way of illustration and examples for purposes of clarity of understanding, it will be apparent to those skilled in the art that certain changes and modifications may be practiced without departing from the spirit and scope of the invention, which is delineated in the appended claims. Therefore, the description should not be construed as limiting the scope of the invention.

All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entireties for all purposes and to the same extent as if each individual publication, patent, or patent application were specifically and individually indicated to be so incorporated by reference. 

1. A method for manufacturing a heat exchanger, comprising integrating modification of one or more substrate surface of the heat exchanger with manufacture of the heat exchanger, wherein one or more substrate surface a heat exchanger is modified with a surface modification material, and wherein the surface modification is performed prior to completion of manufacture of the complete heat exchanger structure.
 2. The method according to claim 1, wherein said modification of one or more substrate surface comprises: (a) depositing the surface modification material on the one or more substrate surface of the heat exchanger; (b) treating the deposited surface modification material to remove moisture, an anionic compound, a binder, and/or a solvent; and (c) optionally, depositing a second layer of material onto the surface modification material to provide one or more functional properties to the surface.
 3. The method according to claim 2, wherein the surface modification changes the wettability, ultraviolet (UV) protection, corrosion resistance, surface energy modulation, and/or aesthetic modification, in comparison to an identical substrate surface that does not comprise the surface modification.
 4. The method according to claim 1, wherein the heat exchanger is a microchannel heat exchanger (MCHE).
 5. The method according to claim 1, wherein the substrate surface comprises a surface of a manifold, a fin, a tube, and/or a microchannel.
 6. The method according to claim 1, wherein said modification of one or more substrate surface comprises an additive barrier coating method, a conversion coating method, or a combination thereof.
 7. The method according to claim 1, wherein the manufacturing method comprises a brazing step and a step for attachment of fluidic interconnects, and wherein the surface modification is conducted either (a) after brazing and prior to attachment of the fluidic interconnects, or (b) prior to brazing.
 8. (canceled)
 9. The method according to claim 1, wherein the manufacturing method comprises a brazing step, wherein flux material is applied to the substrate surface prior to brazing, and wherein the surface modification and flux brazing are conducted concomitantly.
 10. The method according to claim 9, wherein either (a) the surface modification material comprises a metal oxide, and wherein, during brazing, the flux material interacts with the substrate surface to remove native surface oxide and interacts with the surface modification material to remove at least a portion of the metal oxide comprised in the surface modification material, or (b) during brazing, the flux material interacts with the substrate surface to remove native surface oxide and does not interact with the surface modification material.
 11. (canceled)
 12. The method according to claim 1, wherein the surface modification material is an inorganic material.
 13. The method according to claim 12, wherein (a) the surface modification material comprises a metal and/or a metalloid, (b) the inorganic material comprises one or more element that forms alloys with aluminum, and/or (c) the surface modification material forms alloys with aluminum that melt below 660° C.
 14. The method according to claim 13, wherein the surface modification material comprises a metal and/or metalloid, and wherein the metal and/or metalloid comprises a transition metal, a post-transition metal, a lanthanide, an actinide, an alkaline earth metal, an alkali metal, and/or another metal.
 15. (canceled)
 16. The method according to claim 13, the inorganic material comprises one or more element that forms alloys with aluminum, and wherein one or more element comprises silicon, zinc, magnesium, manganese, indium, copper, germanium, calcium, cerium or a combination thereof.
 17. (canceled)
 18. The method according to claim 1, wherein the surface modification material (a) forms a nanostructured material on the substrate surface, (b) acts as a braze, flux, barrier coating, functional coating, or a combination thereof during manufacture of the heat exchanger, and/or (c) is involved in the adhesion of parts of the heat exchanger. 19.-20. (canceled)
 21. The method according to claim 18, wherein the surface modification material is involved in the adhesion of parts of the heat exchanger, and wherein the parts are adhered by brazing, ceramic bonding, or a combination thereof.
 22. The method according to claim 21, wherein the parts are adhered at a temperature lower than 660° C.
 23. The method according to claim 22 wherein the substrate comprises a metal alloy, a ceramic, a polymer, or a combination thereof.
 24. A heat exchanger that is manufactured according to claim
 1. 25. The heat exchanger according to claim 24, wherein the heat exchanger is a microchannel heat exchanger (MCHE).
 26. The heat exchanger according to claim 24, wherein the surface modification material (a) reduces the condensate droplet adhesion force and in turn the wettability of the surface, (b) provides improved heat exchanger performance in comparison to a heat exchanger that comprises an identical substrate surface that does not comprise the surface modification material, (c) provides improved corrosion resistance in comparison to a heat exchanger that comprises an identical substrate surface that does not comprise the surface modification material, (d) provides a reduced amount of holdup liquid in the heat exchanger in comparison to a heat exchanger that comprises an identical substrate surface that does not comprise the surface modification material, (e) reduces the amount of water, condensate, frost, or ice that is maintained within the heat exchanger body during operation in comparison to a heat exchanger that comprises an identical substrate surface that does not comprise the surface modification material, and/or (f) reduces the amount of debris or fouling material which is maintained within the heat exchanger body during operation in comparison to an uncoated heat exchanger surface. 27.-28. (canceled)
 29. A system comprising a heat exchanger according to claim 24, wherein the system comprises an air conditioning system, a refrigeration system, a filter element, or a heat pump. 30.-32. (canceled)
 33. A system comprising a refrigeration unit that comprises: a compressor; an evaporator coil; a condenser coil; a working fluid expansion device; and an enclosure, wherein at least one of the evaporator coil and the condenser coil comprises one or more microchannel coil(s), wherein a surface of at least one of said microchannel coil(s) comprises a coating of a surface modification material that comprises a metal oxide and/or metal hydroxide, and wherein the enclosure comprises a housing that protects the refrigeration unit and maintains a desired temperature range within an area in which the system controls the temperature, wherein the temperature is controlled across variable seasonal temperature conditions in the surrounding environment outside of the area in which the system controls the temperature.
 34. A system comprising a heat pump system that comprises: a compressor; a first microchannel coil; a second microchannel coil; a working fluid expansion device; and an enclosure; comprising both a heating and cooling mode, wherein the first and/or the second microchannel coil comprises a coating of a surface modification material that comprises a metal oxide, and wherein the enclosure comprises a housing that protects the heat pump system and maintains a desired a temperature range within an area in which the system controls the temperature, wherein the temperature is controlled across variable seasonal temperature conditions in the surrounding environment outside of the area in which the system controls the temperature.
 35. (canceled)
 36. The system according to claim 33, wherein (a) said coating of surface modification material comprises a thickness of less than about 20 microns, (b) said coating of surface modification material comprises iron, manganese, magnesium, cerium, tin, zinc, or a combination thereof, and/or (c) the surface modification results in a contact angle greater than 120° or less than 30° on said microchannel coil surface, which reduces the aggregation of water, condensate, frost, or ice on the microchannel coil surface in comparison to an identical microchannel coil surface that does not comprises the surface modification. 37.-39. (canceled)
 40. A method for coating a microchannel heat exchanger with a surface modification material, comprising: (a) optionally, etching one or more surface of a heat exchanger; (b) immersing said heat exchanger in a bath comprising a metal salt; (c) optionally, immersing said heat exchanger in a solution of a fluorinated-terminated or alkyl-terminated compound or alkane; and (d) allowing said heat exchanger to dry.
 41. (canceled)
 42. The system according to claim 34, wherein (a) said coating of surface modification material comprises a thickness of less than about 20 microns, (b) said coating of surface modification material comprises iron, manganese, magnesium, cerium, tin, zinc, or a combination thereof, and/or (c) the surface modification results in a contact angle greater than 120° or less than 30° on said microchannel coil surface, which reduces the aggregation of water, condensate, frost, or ice on the microchannel coil surface in comparison to an identical microchannel coil surface that does not comprises the surface modification. 